Project Summary /Abstract Acute kidney Injury (AKI) associated morbidity and mortality is a major clinical problem that involves multiple overlapping pathophysiological mechanisms. Recent observations from our team and others demonstrated that intestinal microbiota modulates AKI outcome, however the underlying mechanism involved in intestinal microbiota-kidney crosstalk, especially during the recovery phase, remain poorly understood. Our working hypothesis for this grant application is that gut microbiota induces specific changes in the kidney T cell population to mediate AKI outcome and recovery. Furthermore, we hypothesize that short chain fatty acids (SCFAs) produced by certain gut microbiota communicate with kidney tissue via specific smell receptors, such as G protein coupled receptor 41 (Gpr41), olfactory receptor 78 (Olfr78) and Olfr558 present in the kidney. To test our hypotheses, we will (AIM 1) immunophenotype kidney immune cells from wild type (WT), antibiotic treated (AB) and germ free (GF) mice at baseline, during the early phase of AKI, and during recovery of ischemic and cisplatin induced AKI. We will conduct mechanistic studies using T cell deficient mice, T cell antibody depletion and adoptive transfer studies targeting select T cells (e.g. CD4, Tregs, CD3+CD4-CD8- double neg) to determine roles of select T cells on microbiome effects on AKI. Metagenomic and metabolomics with focus on immune inflammatory pathways will be measured in AKI and recovery for identification of microbial communities and metabolites. We will also perform colonization studies with specific bacteria, anti-inflammatory stool (from pregnant mice) and probiotics in AB treated, GF and WT mice. Furthermore, effect of endotoxin released from leaking gut on renal immune cells population will be investigated in studies using toll like receptor 4 (TLR4) deficient mice. To study the role of SCFA signaling receptors in intestinal microbiota?kidney crosstalk (AIM 2) we will induce AKI in Gpr41-/-, Olfr78-/- and Olfr558-/- mice to delineate role of SCFA signaling during AKI recovery. We will identify immune cell or resident kidney endothelium/epithelial source of SCFA interaction with Gpr41, Olfr78 and Olfr558 by evaluating kidney and immune cell specific SCFA receptor deficient mice and performing bone marrow transplants. Additionally, SCFA producing bacteria and exogenous SCFAs will be administered to Gpr41-/-, Olfr78-/- and Olfr558-/- mice and its effect examined on AKI outcomes. To make our lab studies more relevant to human AKI, we will (AIM 3) perform metagenomics of pre and post stool samples and blood metabolomics from patients undergoing cardiac surgery to find gut microbiota differences between those that develop AKI and those that are protected. We will investigate the effect of human microbiota from patients that develop AKI in AB treated, GF mice and SCFA receptor deficient mice. Successful completion of these studies will help understand immunological effects of gut microbiota-kidney crosstalk and potentially novel treatment options involving SCFAs and targeting intestinal microbiota, for AKI and recovery.